1. Field of the Invention
The present invention is directed to low loss semi-processed, cold rolled, motor lamination steels and processes for producing such steels.
2. Description of Related Art
Numerous prior patents have issued in the field of electrical and motor lamination steels, disclosing steels and production processes therefor which were developed with the goal of obtaining low core losses and high magnetic permeability. Silicon steels, generally having a silicon content in the range of 3 wt. % and higher, have been used as electrical steels. Such steels are expensive to produce, and require great care and control over the processing conditions. Steels having significantly lower silicon contents have also been proposed, but there continues to be a great need for economical motor lamination steels having significantly improved magnetic properties.
A recently issued patent to Lauer et al., U.S. Pat. No. 5,609,696, is directed to an electrical steel that is disclosed as possessing good magnetic and mechanical properties. This steel is an example of a steel having a very low carbon content, as well as a relatively low silicon content, proposed for use as an electrical steel. The disclosure in the Lauer et al. patent evidences that the processing of the steel will result in the steel having either an austenitic microstructure or a dual-phase austenitic/ferritic microstructure during hot rolling. The Lauer et al. patent attributes the improved magnetic properties to the use of a very light temper reduction of 1.0% (or less) thickness reduction, as compared with more traditional temper rolling with thickness reductions on the order of 3-8%.
For certain applications, low loss motor lamination steels are required to have a maximum 1.74 W/# (watts/pound) core loss, and a minimum of 2000 G/Oe (Gauss/Oersted) magnetic permeability. In such applications, the steel sheet used will have a nominal thickness of 0.0185", alternatively referred to as 26 gauge steel sheet. Lauer et al. discloses that the steels obtained therein have good magnetic properties, however the steels disclosed in Lauer et al. have core losses that far exceed the core loss maximum (1.74 W/#) in the above-noted requirement.
Numerous other patents and publications exist which are directed to low loss electrical or motor lamination steels. None, however, teach or suggest the product and process of the present invention, in which the motor lamination steel meets the above-mentioned magnetic property requirements.
It is a principal object of the present invention to provide a low loss motor lamination steel having improved magnetic properties, wherein the steel is fully ferritic upon solidification and remains ferritic throughout the processing into a final product.
It is an additional principal object of the present invention to provide a low loss motor lamination steel that minimizes the use of alloy additions to thereby further improve the magnetic properties of the steel.
It is a further principal object of the present invention to provide processes for producing a low loss motor lamination steel having magnetic properties which have a maximum 1.74 W/# core loss and a minimum 2000 G/Oe permeability.
It is a further important object of the present invention to provide a steel and processes for making the steel in which the final grain size is maximized, and in which the {hkl} textures are minimized, with the {hk0} and {h00} textures maximized.